Proper break-In procedure

[85YZRacer]

hey there,
I have a question regarding the correct way to break-in a 2-stroke. I keep reading different break-in procedures from different mx sites. I read about one way where you let the bike idle for 10 min and let it cool down and then you do that same thing for a second time. then you're suppose to ride under a load at 50% throttle and then work your way up from there. Then I read from another motocross site that you're suppose to constantly rev the bike (not leting it idle at all) until it gets to operating temperature and then let it cool down completly. your suppose to do this twice and then ride under a load. So what is the real way to do this? Also, what oil/gas mixture do I run for the break in?

Here is a link to show you what i'm talking about.
http://www.motobutton.com/phpBB2/viewtopic.php?t=7954

 

[MikeT]

I think you should let the bike warm up completely then just ride it normally. Don't baby it. I think that works best.

Also I would just run the normal 32:1 mix ratio. I have used this method for years and haven't had a problem or ever had a piston come out looking bad.

 

[adam728]

If you ask ten people you'll get 10 different opinions. There is no solid, absolute, right answer.

My personal method.

• Start bike and let it warm up till the tops of the radiators are quite warm (around 5 minutes). Mixture of idle and blipping the throttle, no big time reving.
• Let bike cool, at least 1 hour, usually 2+ hours.
• Repeat the two steps above.
• Go ride, take it fairly easy. "Easy" doesn't mean lugging around in 6th gear at 1 mph. Use the entire rpm range, and even short bursts of full throttle are ok as well. Just no lining up and drag racing up a 1/4 mile long sand hill.
• I like to ride for 20 minutes or so, then let the bike cool completly again and repeat. After that, it's broken in.

The heat cycling at the top of the list is quite important. As the engine is thermocycled many things change, seals improve, bearing surfaces are broken in, piston/cylinder are stress releaved a bit. An engine that was jetted great may run lean during the first run cycle because of the above changes that take place. So if you are one of those "jump on it and let it rip" guys you stand a far greater chance of skuffing a cylinder.

 

[76GMC1500]

Heat cycling wont break-in bearings. Rolling element bearings don't break in, anyways. Rolling element bearings shouldn't wear at all within their lifetime (ideally, rolling element bearings fail due to fatigue, spalling, and not wear). If the bike is rebuilt, the cylinder has already been thoroughly stress relieved through heat cycling. The only reason I can think of for letting it cool off is that there is more friction between the rings and cylinder. I say start it and run it light for a bit. Then, shut it down for 15-30 minutes to let everything cool. Start it up and cruise around a bit, run it just hard enough to keep it clear. Then, you're good to go.

 

[adam728]

Heat cycling wont break-in bearings. Rolling element bearings don't break in, anyways. Rolling element bearings shouldn't wear at all within their lifetime (ideally, rolling element bearings fail due to fatigue, spalling, and not wear).

Ideally yes, but this is the real world, where things wear, and where brand new bearings do not have perfect surfaces and do in fact break in. Now, if you don't change the bearings then there is no break in. But new bearings are tighter than ones that have been run in.

As for heating/cooling, it is fairly important even with an old cylinder. Up to 80% of the heat carried away from the piston is handled by the rings. New rings that are not yet seated have a smaller surface area in contact with the cylinder walls, meaning they can't transfer heat nearly as well. Now, that doesn't mean you are going to overheat and melt the piston crown. But it does mean things are running at higher than "normal" temperatures. We regularly see spark pleg temperatures drop 20-30 degrees after a good hour or so of break in. Hp will also come up 5-10%, sometimes more if the engine was very tight when new (which more than likely meant out of spec components).

 

[CRazy250]

ride bike and let it see all of the power band up to 3/4 throttle but never hold it at a constant rpm, after 45 mins it should be good.

 

[freeridingfool]

If you ask ten people you'll get 10 different opinions. There is no solid, absolute, right answer.

My personal method.

• Start bike and let it warm up till the tops of the radiators are quite warm (around 5 minutes). Mixture of idle and blipping the throttle, no big time reving.
• Let bike cool, at least 1 hour, usually 2+ hours.
• Repeat the two steps above.
• Go ride, take it fairly easy. "Easy" doesn't mean lugging around in 6th gear at 1 mph. Use the entire rpm range, and even short bursts of full throttle are ok as well. Just no lining up and drag racing up a 1/4 mile long sand hill.
• I like to ride for 20 minutes or so, then let the bike cool completly again and repeat. After that, it's broken in.

The heat cycling at the top of the list is quite important. As the engine is thermocycled many things change, seals improve, bearing surfaces are broken in, piston/cylinder are stress releaved a bit. An engine that was jetted great may run lean during the first run cycle because of the above changes that take place. So if you are one of those "jump on it and let it rip" guys you stand a far greater chance of skuffing a cylinder.

same method i used and seemed to have a good impact on the new engine

 

[MikeT]

Funny, I'm starting to wonder if it really matters. I break the bike in one way and have been for 23 years with no problems and you guys do it totally different. Neither one of us has had problems. Maybe it doesn't matter as long as you use good oil and warm it up before you get on it.